This invention relates to a rotary actuator and, particularly to a rotary actuator adapted for use as a device for driving an adjusting mechanism of a hydraulic damper of the adjustable damping force type.
A hydraulic damper of the adjustable damping force type is widely used in a vehicle such as an automobile so that the damping force of the hydraulic damper can be adjusted in response to the condition of the road and to operating conditions of the vehicle. The mechanism for adjusting the damping force usually comprises a rotatable adjusting member for adjusting the opening of a liquid passage in the damper and a device for driving the adjusting member. Conventionally, a reciprocatingly movable solenoid connected to a rack-pinion device, a geared motor or the like have been utilized as the driving device for attaining high accuracy in locating the adjusting member. Recently, it has been found desirable to reduce the size for improving the mounting characteristics and to increase the operating speed. However, the reciprocatingly movable solenoid or the geared motor of prior art cannot satisfy the aforesaid desiderata since it is difficult to reduce the size of the motion conversion mechanism or the speed reduction mechanism utilized with the solenoid or the motor and the control circuit necessary for attaining the desired accuracy is complicated.